Preparation of phthalocyanine pigments



United States PatentO PREPARATION JHiTHALOCYANINE PIGMENTS John W. East'es, Ridley Park, Pa., and'Theodore F. Cooke, Martinsville, N. J assignors to American Cyanamid Company, New- York,.N.- Y., a corporation of Maine Ne Drawin t it Original application January 8, 1952, SerialNo. 265,522. Dividedandthisapplication November z ,1953;*Serial Nofi389,853

7 Claims. (Cl. 260 -3145) This invention relates to the preparation of improved l zphthalocyaninez pigments and more particularly to an improved process of finishing metal phthalocyanine in a finely-divided form exhibiting high tinctorial strength and tincto'rialwstability in aromatic solvents.

- Cruder essentially chlorine-free copper phthalocyanine is-i'solated from. reaction mixtures in the stable alpha -cry stal.;form. The crystals are in the form of large, long needles, which haye no tinctorial strength and consequently the :crude phthalocyanine: has no pigmentary value.

Thergenerally accepted-method of producing a finished phthalocyanine pigment has been to subject the crude pigment-to acid-pasting. This process involves. dissolving the pigment in concentrated sulfuric acid, followed by drowningin water to precipitate the pigment. This procedure produces a pigmentary product in a fine state of subdivision having a particle size of the order of a fraction -of a mi cron. lnsthe process, the product is transformedinto the unstable or'beta crystal form and the shade of the blue pigment is reddish blue and the pigment hash'excellent tinctorial. strength.

-Because of the polymorphic character of the phthalo- .cyanines, however, this unstable beta form reverts to "the al ha form When exposed 'to aromatic solvents such as benzene or toluene which are customarily used as 'vehi'cles in paint, enamel. and lacquer systems in which the color is employed'as a pigment. This reversion to the alphatform-causesthe-crystals to increase-in size to such a"d'e'gr'ee'that"the phthalocyanine can no longer be considered at 'pigment asthe strength is only about 2030% of-that before the transformation. Consequent- Tly; the'tinctorial' value of the coating composition is fde'stroyed. h I 'The'" problem'of'crystal growth of the phthalocyanine inaromaticso1ventswas solvedby'Wiswall, as disclosed in the United States Patent No. 2,486,351, and by Loukomsky, as disclosed in United States Patent No. 2,486,- 304, wherein the phthalocyanine was either exposed to the action of a crystallizing liquid such as xylene or toluene and then reduced to a fine particle size by grinding with a grinding aid, followed by re-exposure to the liquid, or wherein the phthalocyanine grinding aid and the crystallizing liquid were subjected to an intensive mixing operation. In both of these processes, the crystals are converted into particles of pigment dimension in the stable alpha form and the particles are stable to crystal growth in aromatic solvents and, therefore, the pigment may be incorporated into coating composition containing these solvents and stored for prolonged periods of time without any change in crystal size and consequently with no diminishing of the tinctorial strength of the pigment. In the Wiswall and Loukomsky processes, the shade of the blue pigment is shifted substantially toward the green.

For many purposes, it would be desirable to produce a reddish shade of the blue pigment, such as is produced by the regular acid-pasting operation, but which can be treated so as to become stable to crystal growth in aromatic solvents without entailing a shift in shade toward the green.

The present invention relates to a process of treating metal phthalocyanines prepared by a particular process in a manner such that a noncrystallizing, red shade, beta form phthalocyanine pigment is produced.

Essentially, the process of the present invention involves preparing a slurry of a metal phthalocyanine,

whichshasz'been prepared in 'anrautoclave in a saturated hereinafter, heating the slurry, du'ringawhich'rtime thes-pig- -mentslurry becomes thick and viscousythen thereafter filtering, washing and drying the pigment. During-this treatment the pigment is swelled and perhaps there is an adsorption of the stabilizing agentas a protective-coating on the pigment. The mechanism of this reaction isrnot understood and, thereforegthe present -invention.-.is- 'not limited to any particular theory "of action. At. any rate, the resulting pigment has outstanding-resistance-to crys talization in aromatic solvents as evidenced by: the fact that the new product has even been boiledin xylene for eight hours and it has been soaked in toluene atj54 C. for over a year without'any indication of 'lossiin strength or any evidence of change'in crystal'for'm.

As such, these newpigments"are ideally"suitcd 'for incorporation in paints, enamels,'inksjlacquers- 'an'd"the like, Whichcontain aromatic solvents and 'suchflcompositions may be stored indefinitely"withdut' exhibiting "any substantial change in color value or loss' in tinctorial strength.

The crystallization resistance possessed by theproducts of this invention is important when it is considered that an untreated conventionally prepared acid-pasted phthalocyanine pigment has virtually no resistance to. crystallization in aromatic solvents. Such conventionally prepared pigments change crystal-form in boiling: xylene in less than. 15 minutes with an accompanying loss of pigment strength to about 20% oftheir initial value.. Moreover, such conventionally prepared pigments lose 50% oftheir strength dueto change in crystal"formafter-only-64 hours exposure in toluene at54 C.

We have foundthat only thosephthalocyanine-pigments prepared in an autoclave in: a saturated alicyclic hydrocarbon solvent, representative exampleswof which phthalocyanines prepared in accordance with the specified process and treated as disclosed herein have outstanding resistance to crystallization as pointed out above.

The stabilizing agents that we have found to be effective in imparting noncrystallizing properties to the metal phthalocyanine pigments prepared as stated hereinbefore are alkyl substituted areas, such as octadecyl urea, lauryl urea, hexadecyl urea, or N-octadecyl-N',N'-ethylene urea.

The amount of stabilizing agent used is not unduly critical. In general, we have found that good results are obtained if 1-10 parts by weight based on the weight of the pigment present are employed.

A solvent for the stabilizing agent may be used. The choice of the solvent is in no Way critical except that it should be nonreactive with the stabilizing agent and should preferably have a boiling point somewhat higher than the temperature at which the reaction is carried out. Aromatic hydrocarbons such as xylene or toluene have been used with good results. Diamyl ether has also been used satisfactorily.

We have found xylene to be particularly effective in making up the pigment slurry because when it is stripped from the slurry by steam, the operation produces sufficient heat to cause completion of the reaction between the pigment and the stabilizing agent.

It is a necessary feature of the stabilization treatment of the present invention that the stabilizing agent-pigment mixture be heated. The length of time the mixture is heated is not unduly critical. In general, satisfactory results are obtained if the stabilizing agent-pigment-solvent mixture is brought to 110 C. and held for a time. As stated hereinabove, if xylene is used as a solvent for the stabilizing agent, the removal of the xylene by steam stripping produces the necessary heat required for the completion of the reaction. However, it has also been found that satisfactory results may be obtained by heating the pigment and stabilizing agent together at higher temperatures, such as around 140 C., in the absence of a solvent.

The pigments treated as specified in the following examples were tested for resistance to crystallization by either the boiling xylene test or exposure to toluene, or both. In the boiling xylene test, the pigment was placed in xylene which was brought to a boil. The pigment was inspected microscopically at intervals to determine if any long needle crystals of the alpha form were forming. At the end of the boiling period, the pigment was filtered from the xylene suspension, dried and ground in a Hoover muller. Ink pulldowns were then made to determine the tinctorial strength of the pigment. In the toluene test, 1

part of the pigment was suspended in 20 parts of toluene which was maintained at 54 C. From time to time the pigment was examined microscopically to determine if there had been any change in crystal form. At the end of the test, the pigment was filtered, dried and tested for strength as described above. The results were confirmed by X-ray diffraction examination to determine if there had been any reversion to the alpha crystal form.

The following examples are illustrative of the present invention, all parts being by weight unless otherwise specified.

Example 1 50 parts of copper phthalocyanine, prepared by the process disclosed in U. S. Patent No. 2,318,783, substituting decalin as the solvent for the nitrobenzene used therein, and thereafter acid-pasted, are slurried in 500 parts of technical toluene. 0.5 part of N-octadecyl-NN-ethylene urea are added. The mixture is refluxed at 112 C. and then cooled to 60 C. and is thereafter filtered. The filter cake is dried at 95 C. in a vacuum of mm. of mercury pressure. A sample of the dried pigment is placed in 100 parts of xylene and boiled for 4 hours. The product is stable to the boiling xylene test. Ink pulldowns of the pigment indicate no loss in tinctorial strength as com: pared to the strength of the pigment before being boiled in xylene. The final pigment exhibits the X-ray diffraction pattern of the beta crystal form.

Example 2 One part of octadecyl urea is placed in 50 parts of xylene and 2 parts of copper phthalocyanine, prepared by the process disclosed in U. S. Patent No. 2,318,783, substituting methylcyclohexane as the solvent for the nitrobenzene used therein, and thereafter acid-pasted, are added thereto. The mixture is stirred at room temperathen diluted with 150 parts of xylene and boiled for 6 hours. The pigment is stable to this test and has the same crystal structure as the product of Example 1.

Example 3 The procedure of Example 2 is followed, replacing the octadecyl urea with lauryl urea. The same solvent stable product is obtained.

Example 4 The procedure of Example 2 is followed, replacing the octadecyl urea with hexadecyl urea. The same solvent stable product is obtained.

The terminology used herein in referring to the alpha and beta crystal forms of phthalocyanine blue is in accordance with the nomenclature used by R. H. Kienle in Official Digest, Federation of Paint and Varnish Production Clubs, No. 300, page 48, January 1950.

This application is a division of our application, Serial No. 265,522, filed January 8, 1952.

We claim:

1. The method of producing a finely-divided, tinctorially strong, noncrystallizing, red shade, beta form, metal phthalocyanine pigment which comprises subjecting a. phthalocyanine pigment prepared in an autoclave in the presence of a saturated alicyclic hydrocarbon solvent and thereafter acid-pasted, to treatment with a higher alkyl substituted urea at a temperature of about C. to about C.

2. The method as in claim 1 wherein the urea is octadecyl urea.

3. The method as in claim 1 wherein the urea is N-octadecyl-N',N-ethylene urea.

4. The method as in claim 1 wherein the phthalocyanine is copper phthalocyanine and wherein the alicyclic hydrocarbon is methylcyclohexane.

5. The method as in claim 1 wherein the phthalocyanine is copper phthalocyanine and wherein the alicyclic hydrocarbon is decalin.

6. The method as in claim 4 wherein the urea is octadecyl-urea.

7. The method as in claim 5 wherein the urea is N-octadecyl-N,N'-ethylene urea.

References Cited in the file of this patent UNITED STATES PATENTS 2,262,229 Giambalvo Nov. 11, 1941 2,282,006 Sloan May 5, 1942 2,305,379 Detrick et al. Dec. 15, 1942 2,556,728 Graham June 12, 1951 

1. THE METHOD OF PRODUCING A FINELY-DIVIDED, TINCTORIALLY STRONG, NONCRYSTALLIZING, RED SHADE, BETA FORM, METAL PHTHALOCYANINE PIGMENT WHICH COMPRISES SUBJECTING A PHTHALOCYANINE PIGMENT PREPARED IN AN AUTOCLAVE IN THE PRESENCE OF A SATURATED ALICYCLIC HYDROCARBON SOLVENT AND THEREAFTER ACID-PASTED, TO TREATMENT WITH A HIGHER ALKYL SUBSTITUTED UREA AT A TEMPERATURE OF ABOUT 90*C. TO ABOUT 140*C. 